1. Field of the Invention
This invention relates to electronic engine controls used in conjunction with an automatic transmission.
2. Prior Art
A historic problem with automatic transmissions is the jerk which occurs when the driver tips in (i.e., opens the throttle to accelerate) from closed throttle at a non-zero vehicle speed, usually in a gear where there is no engine braking. This problem has been found to be more pronounced in front-wheel drive cars than in rear-wheel drive cars. Driveline compliance seems to reduce the jerk, and rear-wheel drive cars have more driveline compliance than front-wheel drive cars. Thus, the growing popularity of front-wheel drive cars has accentuated this jerk problem.
At closed throttle, the engine rpm is at idle when there is no engine braking, regardless of vehicle speed. The transmission gearset speed is a function of the vehicle speed and the particular engaged transmission gear. The gearset speed is almost always higher than the engine speed in low gears and at low vehicle speeds. If the driver opens the throttle (tips in), the engine accelerates freely and rapidly because it is decoupled from the rest of the driveline. This rapid acceleration continues until engine speed reaches the speed of the transmission gearset, at which point the driveline lash is taken up and the transmission begins carrying torque. The result is an objectionable clunk or jerk. That is, jerk results from a high rate of rise in axle torque which is caused by the change from negative torque (deceleration) to positive torque (tip in), accelerating the driveline inertia through the lash. Note that tip in jerk still occurs even in higher gears with engine braking, but with far less severity due to the action of the torque converter and the numerically lower gear ratios.
As illustrated in FIG. 1, when vehicle operation is at closed throttle at 15 mph, engine rpm is at 700 rpm at point A and transmission gearset is at 1200 rpm at point B. If the driver opens the throttle, engine rpm rapidly rises to point B, 1200 rpm, and the transmission applies torque to the wheels. Tip in clunk occurs here as the driveline lash is taken up as torque is applied.
Various electronic control functions are known. U.S. Pat. No. 4,346,625 issued to Latsch et al teaches controlling engine roughness. U.S. Pat. Nos. 4,401,073 issued to Furuhashi and 4,474,153 issued to Hanamoto et al teach idle speed control systems which attempt to differentiate between the acceleration conditions for a vehicle and true idle conditions for a vehicle where it is desired to do idle speed control. U.S. Pat. No. 4,520,694 issued to Eschrich et al describes torque reduction on transmission shifts to improve transmission shift quality. However, these patents neither teach nor suggest a solution to tip in clunk occurring when driveline lash is taken up as torque is applied. These are some of the problems which this invention overcomes.